1. Field of the Invention
The invention concerns a method for controlling the air flow of combustion engines with direct fuel injection according to the generic term of claim 1 as well as a device for implementing the method according to the generic term of claim 18.
2. Description of Related Art
The development level and the available implementations of combustion engines with direct fuel injection, in particular according to the generic term of claim 1, are characterized by the fact that the control of the air quantity to be compressed during the compression stroke takes place either by lowering the starting pressure during the intake stroke (Version I) or by early closing of the inlet valve(s) according to the desired load range, also during the intake stroke (Version II).
For Version I, the reduction of the starting pressure in the compression chamber at the start of each compression stroke is achieved by throttling the air flow supplied to the combustion engine upstream of the inlet valve(s). Examples of embodiments of such control of the air flow supplied to a combustion engine are throttle valves, slide valves or control slides (see DE 3720097 A1; DE 19734227 C2, DE 69704595 T2, DE 19502669 C2, DE 19928523 A1, DE 19501150 C2 or DE 10058200 A1). The current load condition of a combustion engine is determined either by measuring the air flow supplied to the combustion engine or by determining the pressure reduction in the air flow supplied to the combustion engine after the respective throttling element. Due to the manner in which this control of the air flow supplied to the combustion engine is implemented, throttling losses occur that reduce the effect of the pressure reduction required for load control during the intake stroke of each cylinder (see Pöhls, Axel: Investigation of a method for controlled exhaust-gas recycling in petrol engines; VDI Verlag GmbH Düsseldorf; Dissertation 2001; IBSN 3-18-345812-8; p 1 or Homburg, Arno: Optical investigation of jet expansion and mixing with direct-injection petrol combustion methods; Faculty for Mechanical Engineering and Electronics, University of Braunschweig; Dissertation 2002; p 12). These losses lead to a reduction of the efficiency, in particular in the partial-load range of the combustion engine (see Weirich, Marko; NOx-reduction by using the SCR method on a petrol engine with direct injection; University of Kaiserslautern, Department of Mechanical Engineering and Process Technology; Dissertation 2001; p3).
Embodiments of Version II with regard to a throttle-free control of the air flow supplied to the combustion engine per work cycle are described in the patent documents DE 19810466 C2, DE 10111991 A1, DE 4341945 A1, DE 19706750 A1, DE 69720356 T2 or DE 3940752 A1, where the supplied air flow is controlled by varying the opening period of the inlet valve(s).